Event processing example

[andrewdavidmackenzie]

Some example that waits for an external event, processes it and then outputs a new one.

Need some generic way of extending the I/O with a declaration of external sources?

Or just a library that provides an impure function to interface with external system?

e.g. a Named pipe could be a simple example, and echo into it from another process.

Read File function should be able to do that, if it would block on reading...

[andrewdavidmackenzie]

Add as an example that is not tested in CI. Maybe test it compiles though